PRACTICAL EXERCISES IN GEOGRAPHY 69 



An interesting feature of this elementary method of latitude de- 

 termination is its novelty to many teachers. It involves nothing 

 that grammar-school pupils who h£\,ve learned by seeing and think- 

 ing, not by recitation, cannot easily apprehend if they are gradually 

 led up to it by a well graded flight of steps ; the steps are not diffi- 

 cult and the flight is not long. The fear that they are so, on account 

 of which many a teacher dreads to introduce fundamental work of 

 this kind into her teaching, only goes to show the obscurity and con- 

 fusion in which the chajjter on so-called "mathematical geogiaphy " 

 is often enveloped. Leave out this forbidding name, teach slowly 

 on the basis of gradually accumulated observations, and the imagined 

 difficulties will disappear. 



The determination of latitude by the altitude of the Pole star should 

 always be preceded by a proof that the star is close to the pole; but 

 even then the sun-circle method is to be preferred as being possible 

 in the daytime. The measurement of latitude involving the sun's 

 declination should not be introduced until the movement of the sun 

 in declination has been followed and its greatest northing and south- 

 ing measured by a simple method given below. 



Size of the Earth. — Nothing has yet been said of the size of the earth. 

 Observations at a single station will not serve to measure the size, but 

 the essence of the method of measurement may be usefully imitated, 

 and, by correspondence between two schools, actual measurement 

 may l^e made, much to the edification of the pupils. Tbe relations of 

 the local horizon to the plane of the sun-circle, as involved in tl)e 

 measurement of latitude, enables the scholar to "see," if not to dem. 

 onstrate, that an angle of one degree must se})arate ttie local liori- 

 zons of two stations on the same meridian, whose latitude differs by one 

 degree. Similarly, if observations of the sun's midday (meridian) 

 altitude were made at two such stations on the same day the alti- 

 tudes would diff"er by one degree. Then, measuring tlie distance 

 along the meridian arc between the stations, a sim{)le projiortion gives 

 the circumference of the meridian circle: 



1° : 360° ; : length of arc : circumference. 



'I'his imitates the metliod employed 1)}'^ P]ratosthenes. Two parties 

 of scholars stationed at the ends of a short meridian arc in a, school 

 yard or in an adjacent common may each determine the noon al- 

 titude of the sun and m(jasur(! tlie distance l)etween their stations 

 in imitation of tlx; gtMiuiiie method ol" earth measurement, and they 



